Nickel based alloys for internal combustion engine valve seat inserts, and the like

ABSTRACT

A nickel based alloy is provided which includes, in weight percentage, 
     carbon from about 2 to about 3; 
     chromium from about 30 to about 40; 
     tungsten from about 12 to about 18; 
     iron from about 3.5 to about 8.5; 
     molybdenum from about 1 to about 8; 
     manganese up to about 0.5; 
     silicon up to about 1.0; and 
     the balance nickel and incidental impurities. The alloy is useful for internal combustion engine valve seat inserts and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a U.S. national application claiming priorityunder 35 U.S.C. §371 to international patent application No.PCT/US99/01743 filed on Jan. 27, 1999, which claims priority, under 35U.S.C. §119, to provisional patent application No. 60/072,800 filed onJan. 28, 1998.

BACKGROUND OF THE INVENTION

1.Technical Field

The present invention relates to nickel based alloys having highhardness and compressive yield strength. Such alloys are especiallyuseful for engine parts such as valve seat inserts. Another aspect ofthe invention relates to part s made of such alloys.

2. Related Prior Art

Nickel based valve seat insert alloys generally have wear resistance,heat resistance, and corrosion resistance superior to those f high alloysteels, and are therefore often used as materials for structural membersserving under severe conditions, such as valve seat inserts. Knownnickel based alloys used for exhaust valve seat inserts, such as analloy identified as J96 and marketed by L. E. ones Company, haverelatively good characteristics, including good hardness and compressiveyield strengths.

SUMMARY OF TH INVENTION

Valve seat inserts made of such known alloys may experience wear in someheavy duty engine applications. Such wear may be caused, in part, by alack of fineness and uniformity in the microstructure of the alloy.Microstructure refers to carbide size and distribution within a matrixmaterial; a finer microstructure has a greater number of smaller carides distributed throughout the matrix material. Such wear may also becaused, in part, by a weak matrix material which does not adequatelysupport the carbides. Therefore, a nickel based alloy having morefineness and uniformity in the microstructure and a high matrix strengthresulting in higher hardness and compressive yield strength isdesirable.

The present invention is a nickel based alloy which has good finenessand uniformity in the microstructure in combination 4 with a high matrixstrength resulting in increased hardness and compressive yield strengthproperties. These properties provide an alloy having increased wearresistance at elevated temperatures. Also, when the alloy is used as amaterial or a valve seat insert, the increased compressive yieldstrength of the alloy provides an insert having improved retention,i.e., the valve seat remains properly seated in the cylinder headcounterbore.

Cobalt-base materials, such as alloy identified as J3 and marketed by L.E. Jones Company, which tend to demonstrate good wear properties, havealso been used to manufacture valve seat inserts. Utilizing the alloy ofthe present invention, goo wear properties may be obtained without theaddition of relatively expensive cobalt material.

In one aspect, the preset invention is an alloy which comprises:

Element Weight Percent Range C from about 2 to about 3 Cr from about 30to about 40 W from about 12 to about 18 Fe from about 3.5 to about 8.5Mo from about 1 to about 8 Mn 0 to about 0.5 Si 0 to about 1.0 Ni andincidental Balance impurities

In another aspect, the present invention is a nickel based alloy whichcontains, in weight percent;

chromium from about 34.0 to about 37.0;

iron from about 5.0 to about 7.0;

molybdenum from about 2 to about 6.25; and

the balance nickel, other alloying elements, and incidental impurities;

wherein the chromium, iron, and molybdenum content of the alloy increasethe fineness and uniformity of the microstructure and increase thematrix strength of the alloy thereby resulting in the alloy havingincreased hardness and compressive yield strength.

In another aspect, the present invention is a cast alloy comprisingchromium, nickel, tungsten, iron and molybdenum, wherein the relativeconcentration of Cr, Ni and W is such that a three-phase eutecticcomposition is capable of forming at a temperature of about 800° C.

The present invention is a substantial modification over existingindustry standard nickel based alloys. One of the modifications overexisting industry standard nickel based alloys may be accomplished byincreasing the chromium and adding molybdenum to the alloy. Themicrostructure of the resulting alloy is much finer and more uniformthan that of existing standard alloys. The molybdenum serves to increasethe matrix and grain boundary strength.

In another aspect of the invention, metal parts such as valve seatinserts are made from the alloy.

In addition to higher hardness and higher compressive yield strength,the preferred alloys of the present invention also tend to have goodwear resistance, good corrosion resistance and good oxidationresistance.

Before embodiments of the invention are explained in detail, it is to beunderstood that the invention is not limited in its application to thedetails of the composition and concentrations of components set forth inthe following description. The invention is capable of other embodimentsand of being practiced or being carried out in various ways. Also, it isunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a nickel based alloy with improvedhardness, compressive yield strength, and wear resistance. The alloy isdesigned particularly for use in internal combustion engine valve seatinserts, but many other applications are feasible. The present inventionis based on experimental findings that hardness and compressive yieldstrength of the nickel based alloys can be significantly increased byincreasing the matrix strength and improving the fineness and uniformityof the resulting microstructure; this may be achieved by increasing thechromium content to higher levels, and by adding molybdenum to thenickel based alloy.

Carbon (C) is present in the alloy in an amount ranging from about 2 toabout 3 weight percent of the total alloy; preferably, at least about2.2 weight percent; preferably, at most about 2.6 weight percent.

Chromium (Cr) is present in the alloy in an amount ranging from about 30to about 40 weight percent of the total alloy. The chromium contentshould be high enough to achieve a three-phase eutectic microstructurewith nickel and tungsten at a temperature of about 800° C. Preferably,the chronium content is at least about 34.0 weight percent. Preferably,the chromium content is at most about 37.0 weight percent.

Tungsten (W) is present in the alloy in an amount ranging from about 12to about 18 weight percent of the total alloy. Preferably, the tungstencontent is at least about 14.0 weight percent. Preferably, the tungstencontent is at most about 16.0 weight percent.

Iron (Fe) is present in the alloy in an amount ranging from about 3.5 toabout 8.5 weight percent of the total alloy; preferably, at least about5.0 weight percent. Preferably, the iron content is at most about 7.0weight percent. Preferably, the Mo and Fe content is controlled so thecombination of iron and molybdenum tends to form an intermetallic Lavesphase Fe₂Mo which strengthens the grain boundaries. The temperature andrelative concentration of Mo and Fe to form a Laves phase may bedetermined by reference to a Fe—Mo binary phase diagram. Such a diagramis shown, for example, on page 2-197 of the ASM Handbook, Copyright1992, Volume 3, which is herein fully incorporated by reference.

Molybdenum (Mo) is present in the alloy in an amount ranging from about1 to about 8 weight percent of the total alloy. Generally, greatermolybdenum increases alloy hardness and decreases carbide size; however,too much molybdenum may result in a brittle product. The weight percentmolybdenum is preferably at least about 2 weight percent. The weightpercent molybdenum is preferably at most;about 6.25 weight percent. Mostpreferably, the alloy contains about 4 to 5 weight percent Mo.

Manganese (Mn) can be added or present in an amount of up to about 0.5weight percent of the total alloy.

Silicon (Si) may be added to or present in the alloy at levels up toabout 1.0 weight percent of the total alloy.

The balance of the alloy is nickel (Ni) and incidental impurities.Generally, the alloy contains at least about 20 weight percent nickel;preferably at least about 30 weight percent.

At 800° C., the matrix material between the carbides preferably containsa three-phase eutectic composition of the elements Cr—Ni—W, whichprovides increased strength. The relative concentration of Cr—Ni—Wnecessary to form a three-phase eutectic composition may be determinedby reference to a Cr—Ni—W ternary component phase diagram. Such phasediagrams are shown, for example, on page 3-48 of the ASM Handbook,Copyright 1992, Volume 3, which is herein incorporated by reference.

In a highly preferred embodiment, the alloy comprises:

Element Weight Percent Range C from about 2.2 to about 2.6 Cr from about34.0 to about 37.0 W from about 14.0 to about 16.0 Fe from about 5.0 toabout 7.0 Mo from about 2 to about 6.25 Mn up to about 0.5 Max Si up toabout 1.0 Max Ni and incidental Balance impurities

Metal parts are either made from the alloy, such as by casting orforming from a powder and sintering, or the alloy is used to hardfacethe parts. Preferably, the alloy is manufactured by casting. Casting isa conventional process in which raw materials are added together andmelted to liquid state, and then poured into a cast mold.

Preferably, the metal parts are valve seat inserts for use in internalcombustion engines.

Data obtained on an alloy embodying the alloy of the invention is shownin the tables listed in Example 1.

Although the alloy is nickel-based, the thermal expansion coefficient ofthe alloy tends to be closer to that of iron than nickel. (The thermalexpansion coefficient of cast iron is approximately 11.5×10⁻⁶ mm/mm ° C.at a temperature of 25-600° C.) This is beneficial because the inserttends to be much hotter than the surrounding material when the engine isoperating. If the thermal expansion coefficient of the insert alloyclosely matches that of the cylinder head alloy, this enables the insertand cylinder head to expand at the same rate, thereby improving insertretention characteristics.

The alloy has good high temperature compressive yield strength whichincreases wear resistance and decreases material yielding duringoperation. Decreased yielding serves to improve insert retention.Preferably, the alloy has a compressive yield strength of at least about110 thousand pounds per square inch (KSI) at room temperature; morepreferably, about 130 KSI at room temperature.

Increased hot hardness contributes to improved wear resistance andprovides a safety factor for inserts which run beyond the normaloperating temperature.

EXAMPLE 1

An alloy embodying the present invention is made, and tested forhardness, thermal expansion coefficient and compressive yield strength.The alloy is manufactured using a conventional induction meltingfurnace. The following materials are employed to make a 60 pound (lb.)heat of the alloy of the invention:

Weight (lbs.) Material 25 scrap alloy of the invention 12.6 Nickel 8.2Aluminothermic Chrome 6 Low Carbon Ferro Chrome 5.8 Densalloy 1.4 Puremolybdenum 0.9 Carbon 0.33 Ferro silicon 0.2 Ferro Manganese

Densalloy is a powdered metal alloy with approximately 90% tungstencontent commercially available, for example, from Voss Metals ofRockford, Ill. The raw materials are added to the furnace first,followed by the scrap material. The materials are heated until they aremelted. once the material is fully molten, a spectrochemical sample ofthe material is taken for chemical analysis. A spectrochemical analysisverifies the following material chemistry:

Weight Percent Element 2.51 carbon 36.47 chromium 15.44 tungsten 6.70iron 4.15 molybdenum 0.48 manganese 0.56 silicon 33.69 nickel andincidental impurities.

The temperature of the metal is then increased to pouring temperatureand stabilized. The molten metal is de-slagged, and inoculationmaterials are added. The furnace power is then increased to full powerfor approximately 15 seconds to fully mix the inoculation materials intothe molten metal. The metal is then poured into a mold.

The Rockwell C (HRC) hardness of the resulting alloy at room temperatureis HRC 54.

In this example, material properties of hot hardness, compressive yieldstrength, and thermal expansion coefficient were measured. The testresults are as follows:

The compressive yield strength of the nickel alloy at differenttemperatures is as follows:

Temperature Strength Room Temp. (75° F./24° C.) 130 KSI 600° F. (315°C.) 115 KSI 800° F. (427° C.) 112 KSI 1000° F. (538° C.) 115 KSI

The hot hardness of the nickel alloy at different temperatures is asfollows:

Temperature Hardness (HV10) 75° F. (24° C.) 756 200° F. (93° C.) 729400° F. (204° C.) 663 600° F. (315° C.) 619 800° F. (427° C.) 612 1000°F. (538° C.) 594 1200° F. (649° C.) 529 1400° F. (760° C.) 438 1600° F.(871° C.) 306

The thermal expansion coefficient of the nickel alloy at differenttemperature ranges is as follows:

Thermal Expansion Temperature (° C.) Coefficient (×10⁻⁶ mm/mm ° C.25-200 10.73 25-300 11.25 25-400 11.58 25-500 11.89 25-600 12.23

EXAMPLE 2

An alloy is made as in Example 1 except a 725 pound heat of the alloywas produced. The following materials were employed:

Weight (pounds) Material 400 Scrap alloy of the invention 108 Nickel 73Aluminothermic chrome 59 Low Carbon Ferro Chrome 51 Densalloy 22.3 FerroMolybdenum 7.8 Carbon 1.7 Ferro Silicon 1.5 Ferro Manganese

A spectrochemical analysis verifies the following material chemistry:

Weight Percent Element 2.58 carbon 35.93 chromium 15.58 tungsten 5.75iron 4.49 molybdenum 0.32 manganese 0.53 silicon Balance nickel andincidental impurities

Valve seat inserts of the alloy of this Example 2 were tested in a sixcylinder turbocharged diesel engine. The engine was equipped with asplit set-up of Example 2 alloy inserts in cylinders 1,3, and 5 and J3(Stellite 3) alloy inserts in cylinders 2,4, and 6. J3 is a premiumcobalt based valve insert material which is known for its exceptionalwear resistance. Each cylinder contains two inserts of the materialsbeing tested (6 inserts total of each material). The engine was run forover 500 hours under rigorous test conditions. After test, total wear ofvalve and insert were measured.

Insert Alloy Wear (inches) Cobalt base alloy 0.001″ or less (for all sixinserts tested) Nickel based alloy 0.001″ or less (for all six ofExample 2 inserts tested)

Based upon these results, it was concluded that the performance of theinsert alloy of the invention was equal to that of the J3 insert alloy.This result validated the objective to develop a nickel based alloyhaving similar wear performance as more costly cobalt base insertalloys.

It should be appreciated that the alloys of the present invention arecapable of being incorporated in the form of a variety of embodiments,only a few of which have been described above. The invention may beembodied in other forms without departing from its spirit or essentialcharacteristics. The described embodiments are considered in allrespects only as illustrative and not restrictive, and the scope of theinvention is, therefore, indicated by the appended claims rather than bythe foregoing description. All changes which come within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. A nickel based alloy comprising, in weightpercentage: carbon from about 2 to about 3; chromium from about 30 toabout 40; tungsten from about 12 to about 18; iron from about 3.5 toabout 8.5; molybdenum from about 4 to about 5; manganese up to about0.50; silicon up to about 1.0; and the balance nickel and incidentalimpurities.
 2. The alloy of claim 1, wherein the alloy comprises atleast about 2.2 weight percent carbon.
 3. The alloy of claim 1, whereinthe alloy comprises at least about 34.0 weight percent chromium.
 4. Thealloy of claim 1, wherein the alloy comprises at least about 14.0 weightpercent tungsten.
 5. The alloy of claim 1, wherein the alloy comprisesat least about 5.0 weight percent iron.
 6. The alloy of claim 1, whereinthe alloy comprises about 4.5 weight percent molybdenum.
 7. The alloy ofclaim 1, wherein the alloy comprises at most about 2.6 weight percentcarbon.
 8. The alloy of claim 1, wherein the alloy comprises at mostabout 37.0 weight percent chromium.
 9. The alloy of claim 1, wherein thealloy comprises at most about 16.0 weight percent tungsten.
 10. Thealloy of claim 1, wherein the alloy comprises at most about 7.0 weightpercent iron.
 11. The alloy of claim 1, wherein the relativeconcentration of Cr, Ni and W is such that a three-phase eutecticcomposition forms at a temperature of about 800° C.
 12. The alloy ofclaim 1, wherein the alloy comprises, in weight percentage: carbon fromabout 2.2 to about 2.6; chromium from about 34.0 to about 37.0; tungstenfrom about 14.0 to about 16.0; iron from about 5.0 to about 7.0;molybdenum from about 4 to about 5; manganese up to about 0.5; siliconup to about 1.0; and the balance nickel and incidental impurities. 13.The alloy of claim 1, wherein said alloy is manufactured by casting. 14.The alloy of claim 12, wherein said alloy is manufactured by casting.15. The alloy of claim 1, wherein said alloy is used to make a valveseat insert for an internal combustion engine.
 16. The alloy of claim 1,wherein the ratio of Mo and Fe is such that an intermetallic Laves phaseFe₂Mo forms.
 17. A valve seat insert for use in an internal combustionengine, said valve seat insert made of an alloy consisting essentiallyof in wieght percent: carbon from about 2 to about 3; chromium fromabout 30 to about 40; tungsten from about 12 to about 18; iron fromabout 3.5 to about 8.5; molybdenum from about 4 to about 5; manganese upto about 0.5; silicon up to about 1.0; and the balance nickel andincidental impurities.
 18. The valve seat insert of claim 17, whereinsaid alloy is manufactured by casting.
 19. The valve seat insert ofclaim 17, wherein the alloy comprises: carbon from about 2.2 to about2.6; chromium from about 34.0 to about 37.0; tungsten from about 14.0 toabout 16.0; iron from about 5.0 to about 7.0; molybdenum from about 4 toabout 5; manganese up to about 0.5; silicon up to about 1.0; and thebalance nickel and incidental impurities.
 20. The valve seat insert ofclaim 17, wherein the alloy consists of, in weight percent: carbon fromabout 2 to about 3; chromium from about 30 to about 40; tungsten fromabout 12 to about 18; iron from about 3.5 to about 8.5; molybdenum fromabout 4 to about 5; manganese up to about 0.5; silicon up to about 1.0;and the balance nickel and incidental impurities.
 21. A nickel basedalloy consisting essentially of in weight percent: chromium from about34.0 to about 37.0; iron from about 5.0 to about 7.0; molybdenum fromabout 4 to about 5; and the balance nickel, other metals, and incidentalimpurities; wherein the chromium, iron, and molybdenum content of thealloy increase the fineness and uniformity of the microstructure of thealloy thereby resulting in the alloy having increased hardness andcompressive yield strength.
 22. The nickel based alloy of claim 21,wherein said alloy is used to make a valve seat insert for an internalcombustion engine.
 23. The nickel based alloy of claim 21, wherein saidalloy has a compressive yield strength of at least about 110 KSI at roomtemperature.
 24. The nickel based alloy of claim 21, wherein the alloyconsists of, in weight percent; chromium from about 34.0 to about 37.0;iron from about 5.0 to about 7.0; molybdenum from about 4 to about 5;and the balance nickel, other metals, and incidental impurities.
 25. Acast alloy comprising chromium, nickel, tungsten, iron and molybdenum,wherein the relative concentration of Cr, Ni and W is such that athree-phase eutectic composition is capable of forming at a temperatureof about 800° C., the alloy consisting essentially of in weight percent:molybdenum from about 4 to about 5, chromium from about 30 to about 40,and tungsten from about 12 to about 18, and the alloy further comprisescarbon from about 2 to about 3 weight percent.
 26. The cast alloy ofclaim 25 wherein the alloy is used to make a valve seat insert for aninternal combustion engine.
 27. The cast alloy of claim 25 wherein theratio of Fe to Mo is such that an intermetallic Laves phase Fe₂Mo forms.28. The nickel based alloy of claim 1, wherein the alloy consists of, inweight percentage: carbon from about 2 to about 3; chromium from about30 to about 40; tungsten from about 12 to about 18; iron from about 3.5to about 8.5; molybdenum from about 4 to about 5; manganese up to about0.50; silicon up to about 1.0; and the balance nickel and incidentalimpurities.